refactoring connectionpool: add healthcheck, move getConnection and first call reBalance outside constructor

pool.go

@@ -46,15 +46,18 @@ type (
 		nodes []*node
 		keys  []uint32
 		conns map[uint32][]*node
+
+		unhealthy *atomic.Error
 	}
 )
 
 var (
+	errBootstrapping        = errors.New("bootstrapping")
 	errEmptyConnection      = errors.New("empty connection")
 	errNoHealthyConnections = errors.New("no active connections")
 )
 
-func newPool(ctx context.Context, l *zap.Logger, v *viper.Viper) (*Pool, error) {
+func newPool(l *zap.Logger, v *viper.Viper) *Pool {
 	p := &Pool{
 		log:   l,
 		Mutex: new(sync.Mutex),
@@ -74,6 +77,8 @@ func newPool(ctx context.Context, l *zap.Logger, v *viper.Viper) (*Pool, error)
 			Timeout:             defaultKeepaliveTimeout,
 			PermitWithoutStream: true,
 		},
+
+		unhealthy: atomic.NewError(errBootstrapping),
 	}
 
 	buf := make([]byte, 8)
@@ -126,11 +131,7 @@ func newPool(ctx context.Context, l *zap.Logger, v *viper.Viper) (*Pool, error)
 			zap.Uint32("weight", p.nodes[i].weight))
 	}
 
-	p.reBalance(ctx)
-
-	_, err := p.getConnection(ctx)
-
-	return p, err
+	return p
 }
 
 func (p *Pool) close() {
@@ -150,7 +151,12 @@ func (p *Pool) close() {
 
 func (p *Pool) reBalance(ctx context.Context) {
 	p.Lock()
-	defer p.Unlock()
+	defer func() {
+		p.Unlock()
+
+		_, err := p.getConnection(ctx)
+		p.unhealthy.Store(err)
+	}()
 
 	keys := make(map[uint32]struct{})
 
@@ -166,8 +172,9 @@ func (p *Pool) reBalance(ctx context.Context) {
 			weight = p.nodes[i].weight
 		)
 
-		if ctx.Err() != nil {
-			p.log.Warn("something went wrong", zap.Error(ctx.Err()))
+		if err = ctx.Err(); err != nil {
+			p.log.Warn("something went wrong", zap.Error(err))
+			p.unhealthy.Store(err)
 
 			return
 		}